This invention relates to an apparatus for machining a bevel gear such as a spiral bevel gear, a hypoid gear or the like.
A conventional apparatus for machining a bevel gear of this kind is disclosed in Japanese Published Examined Patent Application No. 516/1965. The apparatus comprises an apparatus frame, a spindle head provided on the apparatus frame for rotatably supporting a spindle on which a machining tool is mounted, and an indexing unit for supporting a workpiece as a raw material for a bevel gear, thereby machining each tooth space with the machining tool by rotating the workpiece with the indexing unit by one pitch of teeth to be formed on the workpiece. In this apparatus, the spindle is rotatably supported by the spindle head in a posture downwardly inclined towards the indexing unit such that the spindle is movable in an axial line of the spindle. The spindle head is movable in a lateral direction which crosses the axial line of the spindle at right angles, and is rotatable about a perpendicular axial line which crosses at right angles the axial line of the spindle. A movable frame is provided on the apparatus frame in front of the spindle head such that the movable frame is movable in the horizontal forward and backward directions as well as in the lateral direction. The indexing unit is supported on the movable frame such that it is movable up and down along an inclined surface which crosses the axial line of the spindle at right angles. In order to feed the machining tool, the spindle is moved forwards and backwards relative to the spindle head. In order to mount or dismount the workpiece, the movable frame is moved forwards and backwards. In order to change the spiral direction of teeth, the indexing unit is moved by the movement of the movable frame from one side of the lateral direction to the other side and, at the same time, the spindle head is rotated, thereby moving the the cutting point from one lateral side to the other side of the workpiece. In order to change the pitch angle of the bevel gear, the spindle head is rotated and, at the same time, is moved in the lateral direction, thereby changing the angle of inclination of the spindle against the indexing unit.
The conventional apparatus as described above has the following disadvantages. Namely, in changing the spiral direction, the spindle head must be rotated and the movable frame must be moved in the lateral direction, resulting in a complicated work. In addition, the spindle is supported slidably in the axial direction relative to the spindle head and is supported in a laterally movable manner and a rotatable manner via the spindle head on the apparatus frame. Therefore, the spindle has a degree of freedom of as many as three and is liable to give rise to vibrations of the spindle due to looseness or the like in each of the sliding portions and rotatable portion. The lifetime and the machining accuracy of the machining tool are thus likely to be lowered.
In the above-mentioned conventional apparatus, the indexing pitch of the indexing unit is fixed. Therefore, bevel gears of different tooth pitches cannot be machined. As a conventional apparatus in which the indexing pitch can be varied, Japanese Published Examined Utility Model Application No. 58-35387/1983 discloses an apparatus having the following construction. The apparatus has two pieces of indexing plates provided on an indexing shaft on which a workpiece is mounted. Two pieces of Geneva shafts (or geneva movement shafts) are provided, each of the shafts having a Geneva pin which is engageable with slots on an external periphery of each of the indexing plates. Each of the Geneva shafts is connected via a change-over clutch to a driving source. By changing over the change-over clutch, the indexing shaft is rotated at an indexing pitch between that corresponding to one of the indexing plates and that corresponding to the other of the indexing plates. It may be considered to incorporate this indexing apparatus into the above-described apparatus for machining a bevel gear in order to cope with a change in the pitch. However, in this indexing apparatus, it is not possible to change the indexing plates and the Geneva shafts to prepare for the next machining work during the machining of the bevel gear. The indexing apparatus is therefore not suitable for manufacturing various kinds of products respectively in small quantities.